What strikes me in your case is the very poor communication you have with your bfs. Usually people have at least a hint of what's going on when the relationship flounders, or get some explanation from the other. It seems in your case a deeper level of communication is lacking.

In the case of the longer relationship, did you actually talk about each other's feelings, situation, moods, dreams, worries? Seems like he was pretty much a foreigner to you, even after 5 months,... (not that it's so unusual)

Maybe you should spend a bit more time getting to know the next guy before going out with him. It's also not a bad idea to discuss about past experiences. You can see the maturity of someone by the way they talk about past relationships.

Also, is it possible that you are selecting for guys which are reserved and have trouble expressing themselves?